Thats exactly it, Judy! you are quite right about that. Thats just the human nature - to relax when nothing happens, and then boom!!! when you least expect it.
About long lines, Europe has an interesting way to avoid it. I was quite surprised by it actually. Instead of one huge long line infront of all the gates, what they did was put scanners at every gate. That way, only people who are at a certain gate boarding a certain flight go through the security check point at one time. This is better for security too, because the agents are more carefull and can be more scrutinizing, cause they dont have to hurry cause of the long lines. And the security is right before the airplane is boarded.
Of course its less economically efficient for the airport (cause they would have to invest in, say 50 scanners instead of 2 or 5 like we have in most airports), but you get to avoid the long lines and I think the security is better.